Method of depositing elemental material from a low pressure electrical discharge



, .1. 'r. NFF METHOD 0F DEPOSITING ELEMENTAL MATERIAL'FROM Jan. 20, 1970 3,491,015

A Low PRESSURE ELEcTRIcAL DISCHARGE Filed April 4. 1967 mi f mw M mM .w W@ w www United States Patent O 3,491,015 METHOD OF DEPOSITING ELEMENTAL MA- TERIAL FROM A LOW PRESSURE ELECTRI- CAL DISCHARGE John Tom Naf, Costa Mesa, Calif., assignor to Automatic Fire Control Inc., South El Monte, Calif., a corporation of California Filed Apr. 4, 1967, Ser. No. 628,330 Int. Cl. C23c 15/00 U.S. Cl. 204-298 3 Claims ABSTRACT OF THE DISCLOSURE A method of depositing elemental material from a glow discharge supported in an inert argon atmosphere between an anode source and a cathode for receiving the deposit of elemental material. The elemental material is vaporized from the anode source into the discharge by applying an arc plasma jet directly to the source.

This invention discloses and teaches improvements in a source of vaporized metallic and metalloid atoms and ions which are generated at high temperature in an arc device, said arc device being integrally included in a high voltage gaseous glow discharge circuit. This invention is useful in providing an atom and ion source which can be replenished with metallic or metalloid atom raw material on demand, providing an atom vapor source suitable for a long time duration metal vaporization and vapor plating process.

One of the serious limitations on low pressure gaseous glow discharge plating of metals on substrates is the short process operation time, imposed by using thin deposits, or small amount of coatings of the metals to be vaporized, on a thermally heated lament. This invention provides a solution to this problem.

Included in the objects of my invention are:

First, to provide an improved means of continuously generating over long process operating time periods the vaporized metal and metalloid atoms and ions suitable for application in a low pressure gaseous glow discharge metal plating process.

Second, to provide an improved ionized metal atom source for a low pressure, gaseous glow discharge, continuous metal ion plating device.

Third, to provide a high temperature arc source suitable for vaporizing and ionizing metal and metalloid atoms within the electrical eld of a high voltage, low pressure, gaseous glow discharge plating machine, over long periods of time.

Fourth, to provide a replenishable electric arc means source for ionized metal and metalloid ions, integral with a low pressure gaseous glow discharge process for plating said metal and metalloid atoms on a substrate.

Other objects, together with a more complete understanding of my invention, are taught by reference to the following description and claims, which are to be read in conjunction with the following drawings, in which:

FIGURE 1 represents an elevational vperspective and partial sectional view of the low pressure gaseous glow discharge device, incorporating the multiple arcs supplying metal and metalloid vapor.

FIGURE 2 is an enlarged detail elevational sectional and functional electrical schematic circuit view of the multiple arc sources of FIGURE 1, suitable for constructively practicing this invention.

Referring to FIGURE 1, in detail, there is shown an elevational perspective and partial sectional view of the high voltage, low pressure glow discharge apparatus 1, having a gas tight, electrically non-conductive evacuable container 2 sealed by external atmospheric pressure to the non-conductive base plate 3. The low pressure evacuation system 4, is connected to the valve 5 by the pipe 6, and the pipe 7 connects the valve 5 to the base plate 3. The components 2-7 represent prior art teaching.

A streaming argon gas atmosphere of 10400 micron Hg. pressure is maintained in the gas phase 8 during theplating operating of apparatus 1. The cathode plate 9 is adaptively secured in the apparatus 1 by the conductor 10, which in turn is led through a gas-tight, non-conductive seal 11 to the exterior high voltage power source not shown.

The enclosed low voltage DC arc 12 is shown in elevational perspective View, with an exterior arc plasma jet 13 issuing from the arc 12. The arc 12 has an exterior, liquid cooled, electrically conductive anode 14 and an interior, non-conductive cathode cap 15. The electrical conductor 16 carries current through the cathode cap 15, which is typically a porcelain electrical insulator, and the conductor 16 is in turn connected to the exterior atmosphere through the gas-tight, electrical lead-in seal 17. The gas-tight seal 18 lconducts the argon gas inlet tube 19 through the base plate 3 to the cathode cap 1S. The metal cap 41 secures cap 15 to the exterior anode 14. The coolant fluid outlet 20 conducts the coolant, typically water, away from the exterior anode 14 through the gas-tight container seal 21. The exterior anode fluid coolant inlet 22, is led through the base plate 3 to the atmospheric exterior through the gas-tight seal 23. The fluid coolant, typically water, is pumped through the anode uid coolant jacket at a rate suflicient to maintain the arc 12 at the desired temperature, as it removes the excess thermal energy in the heated coolant iluid. The cathode 9 also may be water cooled.

The exterior arc plasma jet 13 forms a transferred jet impinging on the surface 24 of the low pressure glow discharge anode source structure 25. Through the partial cross sectional view of anode structure 25 is shown the vaporizable coating metal 26 in the electrically conductive container 28. The vaporizable coating metal 26 fuses to a molten pool 27 at and below the junction area of the impinging exterior arc plasma jet 13 and the metal 26. The expendable rod 52 is shown supplying the reserve of the metal 26, angularly located above the area of the molten metal pool 27, in order to form a reserve source of the metal 26 which can be metered into the pool 27, on signal. The support arm 29 locates the linear actuator 53 for the rod 52 in the required operating position and is also adapted to enclose and conduct a set of electrical power and signal wires to the exterior of the base plate 3, through the gas-tight seal 30.

FIGURE 2 illustrates the enlarged sectional View of FIGURE 1, detailing the anode vapor source invention. The enclosed low voltage DC arc 12 is shown in elevational operational position relative to the low pressure glow discharge anode source structure 25 and the replenishing expendable metal rod 52. Other replenishing sources of the expendable metal 26 may also serve as a cooperative source of metal 26. In further sectional detail the arc 12 has a cathode cap 15 made of electrically non-electrical conducting porcelain or the like high melting non-conductor. The cap 15 is tightly sealed to the outer water jacket shell 40 by the metal cap 41. A circular opening 55 insulates cap 41 and tube 16. The inner water jacket shell 42 is separated from the outer shell 40 by the helical wound or shaped water passage separator 43, which insures continuously elective water cooling and highly eicient heat removal from the arc 12. The water enters the anode at the inlet 22, winds through the water passage 44 between the outer shell 40, the inner shell 42 and the separator 43.

The water inally exits at outlet 21. The argon gas is metered into the gas inlet tube 19, which is secured to the metal cap 41. The tubular opening 51 pasess the argon gas in the tube 19, venting the gas into the arc plasma opening 46, through the annular ring openings 45. The pointed cathode rod 47 is secured to the cap 15 and is also electrically conductively secured to and encloses the electrical conductor tube 16. The electrical conductor tube 16 is the exterior tube in a pair of hollow coaxial fluid coolant heat transfer tubes, the inner coolant tube 54 is also disposed to conduct fluid coolant. Typically the water coolant is conducted through the exterior tube 16, and exits through the inner water coolant tube 54. The tube 16 also conducts power to the cathode 47.

The metal cap 48 is also aiiixed to the cathode rod 47 and secures the tube 16. The venturi shaped orifice 49 in the nozzle block 50 is sized and shaped to control the argon gas pressure, together with the gas inlet flow rate and the arc electrical performance, to maintain an argon gas pressure of 50-100 mm. Hg in the arc plasma opening 46. The nozzle block 50 has a preferred venturi shaped nozzle approach to the upstream side of the nozzle oriiice 49. The nozzle block 50 is welded to the inner water jacket shell 42. The components 40, 41, 42, 43 and 50 are typically copper metal, selected for use due to its high electrical and thermal conductivity.

The high temperature anode vapor source of this invention produces a high concentration of ionized atoms of the metal 26 in the anode column and arc attachment area and a large high temperature surface area from which the atoms can rapidly evaporate. The anode vapor source of this invention will thus provide the hot ionized atom source for high metal plating speed in the high voltage low pressure glow discharge.

A multiplicity of the anode vapor sources comprising the combination of the anode arc 12 and the anode structure 25 may be grouped in a single low pressure, high voltage plating device. For example, more than one anode arc of the type of arc 12 may be grouped to form transferred arcs to one anode structure 25 type. Or, a multiple number of single combinations of arc 12 and anode structure 25 may be grouped around a large complex shaped structure requiring plating, which is located in the cathodic plate region, thus ion metal plating onto the large complex shaped structure.

The high voltage, low pressure, gaseous glow discharge cathode plate 9 is typically operated in a streaming argon gas atmosphere 8 of 10-100 micron Hg pressure. The plate '9 is operated typically at 4000 DC volts with respect to the anode 25, powered by the DC variable high voltage supply 31, which is regulated through the resistance 32 connected by the wire conductor circuit 36. The arc 12 is anodically connected by its anode 14, at the coolant inlet 22 through a controlling resistance 33 to the anode 25. The DC low voltage power supply 34 drives the arc 12, regulating the current through resistance 35 to typically 50 amperes, and a DC voltage range of 10-30 volts.

In operation the are 12 is supplied with up to 1500 watts at 30 volts DC, using a 50 mm. Hg pressure of argon gas, exiting through the orifice 49 having a diameter of about 0.010 inch. The arc 12 for-ms a transferred 60 jet 13 with the junction area of the metal 26 melting to form the metal pool 27. The molten metal pool 27 acts cooperatively as the volatile metal anode for the high voltage, low pressure glow discharge between anode 25 and cathode 9. Objects to be plated in the glow discharge are placed in the container 2, located in the cathode 9 in the cathode dark space for metallic plating. Metals selected from the group tungsten, tantalum, aluminum, chromium, copper, graphite, gold and silver may be used as sources of vaporizable metal 26.

Obviously many modifications and variations of the improvement in anode vapor sources are possible within the scope of this invention as disclosed and claimed, and the invention may be practiced otherwise than as specifically described.

I claim:

1. A method of depositing elemental Imaterial in a low pressure glow discharge in an argon atmosphere comprising: enclosing a low voltage DC arc plasma maintained in a streaming argon atmosphere, at a gas pressure of 50-100 mm. Hg and generated by a potential in the range of 10-30 volts and a total current not exceeding 50 amperes between an interior cathode and an exterior liquid cooled anode, exiting said enclosed arc plasma through a small orifice in said exterior anode to form an exterior arc plasma jet; forming a transferred arc plasma jet by impinging said exterior arc plasma jet on a low pressure glow discharge anode source structure containing vaporizable elemental coating material and causing said material to evaporate at the impingement junction area of said transferred arc plasma jet; supporting a high voltage, low pressure gaseous glow discharge in an argon atmosphere at a pressure between 10 and 100 microns of Hg between a cathode means, and said anode source structure containing said vaporizing elemental coating material, whereby said material moves through said discharge to said cathode and deposits thereon; and replenishing the source of said elemental coating material at said anode by advancing a consumable solid source into said anode as it is being used.

2. The Imethod of claim 1 wherein said vaporizable elemental coating material is selected from the group consisting of aluminum, copper, chromium, tungsten, tantalum and graphite.

3. The method of claim 1 wherein elemental material is impinged by a plurality of arc plasma jets.

References Cited UNITED STATES PATENTS 2,157,478 5/1939 Burkhardt et al. 204-192 3,140,380 7/1964 Jensen 219-76 3,404,084 10/ 1968 Hamilton 204-298 3,408,283 10/1968 Chopra et al. 204-192 FOREIGN PATENTS 959,472 6/ 1964 Great Britain.

ROBERT K. MIHALEK, Primary Examiner U.S. Cl. X.R. 

